Collective light shifts of many longitudinal cavity modes induced by coupling to a cold-atom ensemble

TL;DR

This study demonstrates collective light shifts across many cavity modes induced by a large cold-atom ensemble, revealing complex cavity-atom interactions and bistability, advancing multifrequency cavity QED research.

Contribution

It experimentally shows simultaneous shifts of over 100 cavity modes caused by a cold atom cloud, extending cavity QED beyond single-mode interactions.

Findings

Significant collective light shifts of ~100 cavity modes

Observation of bistability in cavity transmission spectrum

First experimental evidence of multifrequency cavity QED effects

Abstract

We experimentally study the interaction between a cold atom cloud and many longitudinal modes of a high quality Fabry-Perot cavity, by measuring signatures of collective light shifts in the cavity transmission spectrum of an optical frequency comb probe. Using a resonator coupled to more than $10^5$ intracavity atoms, we detect significant shifts of $\sim 100$ cavity modes simultaneously, which is a direct manifestation of physics beyond the hitherto explored regime of cavity-cold atom interaction with only single or few longitudinal modes at a time. For the cavity mode closest to the atomic resonance, we demonstrate a bistability in the transmission spectrum, arising due to a combined coupling of the cloud to an external pump laser and a cavity mode probed by the optical frequency comb. These results provide a first step toward deeper exploration of multifrequency cavity quantum electrodynamics, where ultrashort pulsed sources could be used for optical manipulation, cooling and entanglement of cold atoms in a resonator.